Saving Data Problem

I want to save datagridview data in Excel sheet as per user spcify the location for that I write some code but It's not working properly. If I spacify the location in the code then It alway overwite the data on previous data. In Savedialog Box when I spcify the location It create a Excel File but can not open. Other wise It Save that file and again show the savedialogbox with the name of Book.